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Thursday, November 6, 2008

Surface sampling from Titan balloon

Space.com has an article on the possible ESA Titan balloon contribution to a Flagship Titan Saturn System mission http://www.space.com/scienceastronomy/081106-am-titan-balloon.html.

The article states that the balloon gondola will have the ability to float and lakes while the mission will have the ability to grab and then analyze surface samples. This would be great if it's true, but I have my doubts. While it is easy to have a balloon descend to the surface, it is much harder to prevent damage to the gondola and balloon if winds drag them across the surface. Perhaps this is some kind of snake that would be tolerant of dragging across the surface that would be lowered to the surface to grab samples.

These low ground maneuvers would be that much harder to manage with Titan a long distance away (I forget how long it takes a radio wave to travel the distance) and the orbiter only occasionally in direct contact with the balloon (even when the orbiter has reached Titan orbit).

Anyone know anything more about this?

On the bummer side, the TSSM mission would arrive in the Saturn system in 2030. That would make me only 74 on arrive and about 76 when it finally reaches Titan orbit. Whichever flagship destination is chosen (Titan or Europa), this will be my last outer planet flagship mission. I suddenly feel a lot older...

Actually, the Europa mission -- assuming a launch in 2020, like the Titan mission -- would reach Jupiter in only 5 years rather than 10 (and then, like the Titan mission, spend about 2 years cruising the planet's moon system before braking into orbit around its final target). In any case, these things take a long time. You and I will be old geezers before either of them can arrive at its destination, Van -- which is another reason why I find myself wondering about possible cheap missions that could fly at about the same time and duplicate some of the science scheduled for the other Flagship mission.

In that connection, have you noticed that a low-cost Saturn flyby mission equipped with either Saturn entry probes or a short-lived Titan boat could also make a flyby of a Jovian Trojan on the way out to Saturn (if, of course, it doesn't utilize a Jovian gravity-assist flyby)?

Actually, according to Curt Niebur's presentation to the Planetary Science Subcommittee last month ( http://www.lpi.usra.edu/pss/presentations/200810/opf.pdf ), the Titan mission would take only 9 years -- not 10 -- to reach the Saturn system. (It would use a SEP stage ejected partway through the Asteroid Belt, rather than a Jupiter gravity-assist flyby.) Still not much consolation, I know...

As for the Europa Flagship: not only would it reach its target faster, but Niebur indicates that its launch could occur any time in "2018-2022".

There's been one odd change since his last report to the PSS in June ( http://www.lpi.usra.edu/pss/presentations/200806/04niebur.pdf ). In that one, he said that both the Titan Balloon and Lander would be dropped off before the main craft braked into Saturn orbit. In the October report, he says that the Balloon would be "released on the first Titan flyby, and the Lander on a subsequent flyby". Either way (as he explicitly says in June), the Balloon and Lander would have to send all their data back for a very long time either direct-to-Earth and/or by relay through the Orbiter in Saturn orbit -- the latter presumably possible only when it was fairly close to Titan. Since he specified a minimum lifetime of only 6 months for the Balloon and 1 month for the Lander (if it's dry-land), this means that there's a good chance that by the time the Titan Orbiter got into Titan orbit there would be nothing left for it to relay data back FROM. But then, even after arrival in Titan orbit the Orbiter's path over Titan would allow it to pass over either the Lander or the Balloon every 8 days or so -- so either in-situ craft must clearly have a big data-storage capacity in any case. Unless, again, they go for a short-lived lake Lander that would spew all its data back during a single Titan flyby by the main craft -- and in fact Niebur in October and Jonathan Lunine at the recent Europlanet Conference say flatly that ESA has decided to land in a lake rather than on dry land. You'd think that in that case the logical thing would be to release the LANDER first, and then release the Balloon only just before the main craft puts itself into orbit around Titan.

Actually, Lunine -- http://www.cosis.net/abstracts/EPSC2008/00621/EPSC2008-A-00621-2.pdf -- also says the Titan mission might be launched as early as 2018, and confirms that the main craft would make its Enceladus flybys "with instrumentation for plume sampling well beyond Cassini capability", although he doesn't mention anything specific about being able to use the mass spectrometer to analyze solid plume grains.

One more note: opportunities to reach Saturn via a Jupiter gravity-assist come along every 20 years. In fact, the proposed New Frontiers mission with dual Saturn entry probes would be launched in Dec. 2015 and reach Saturn that way as early as March 2022! ( http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/39758/1/06-1824.pdf .) You could of course do the same thing with a flyby craft with Titan boat. Or -- if such a Titan boat mission turned out to be New Frontiers-class rather than Discovery-class -- you could do it with a solar-powered main craft. (It's interesting, in this context, that the official -- as opposed to draft -- release of the New Frontiers 3 Announcement of Opportunity is set for next January, which is the same month that NASA officially decides which Outer Planets Flagship to fly. Does this open a tiny window of opportunity for a Titan Boat mission to be included on the NF3 AO's list of acceptable missions? Or am I just a fool in love?)

Getting (finally) to your original question: I think the Space.com reporter got mixed up -- that "helicopter rotor", "floaters" and "scoop" are all accessories for the separate ESA Titan lander, not the balloon. The helicopter rotor is the only one that doesn't sound plausible to me; even given the very easy flying conditions on Titan, you'd need a big power source and I can't see the ESA putting one on a lander at this stage of development.

Now, in the talks from the OPFM Instrument Workshop in June -- http://opfm.jpl.nasa.gov/community/opfminstrumentsworkshoppresentations/ -- Athena Coustenis really is still going on about the possibility of having the Balloon be able to swoop down to the surface and use a tether and sampling system -- and in fact this same possibility was mulled over by Jonathan Lunine's Titan mission design team a few years ago. But Lunine & Co. were working on the assumption that there wouldn't be a separate Lander, and they pretty quickly reached the conclusion that a combination of a separate lander and a non-landing balloon was vastly more workable. Sure enough, in his presentation at the OPFM Instrument Workshop, ESA's Christian Erd says (pg. 18) that the Balloon would hover at 10 km, with "near-surface operation optional". (I still remember Dick Spilker telling me sourly over the phone that he would soon have to go to Toulouse and tell the ESA's gang that their original concepts for the Titan-Enceladus mission -- and, no doubt, for the Europa-Ganymede mission as well -- were wildly over-optimistic. I imagine that ExoMars is, too, and the ESA is currently running head-on into that fact.)

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.